Managing Limiters: preparing to race in the Kona heat

author : Curt Chesney
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Core temperature, hydration, liquid absorption and sweat rates: how they affect racing in the heat

By Curt Chesney
D3 Multisport

After placing ninth overall at Ironman Lake Placid in 2009 I decided to give Kona another shot. I had toyed with the idea for a couple of years but with two bad races there on my record, I was having trouble wrapping my brain around racing well at the big show.

Ironman Hawaii is unlike any other IM race. I raced there in 2001 and was not happy with my race, but looking back on my limited experience and knowledge at the time, I think I did OK. In 2005, I should have had more experience but I made every mistake possible and had to walk it in on the second half of the run. I’ll just call that one a complete lack of respect for the course and conditions.

My reason for wanting to race in ‘09 was that I needed to find something in triathlon that would really challenge me. Kona seemed like the puzzle that I had not yet deciphered. My preparation for ‘09 was going well but work commitments got in the way two weeks from the race, and there was no way I could make the start line. I was bummed for sure, but the positive side was that it made me motivated and hungry for success in 2010.

So now I was looking at having a full year to prepare myself for Kona. Since 2005, I had learned many things about my racing. The most important was that my sweat rate was the highest I have come across. I have measured as high as 96 oz. per hour on an 85 degree day. At least now I knew why I struggled in hot races.

Over the winter I did as much research as I could on racing in the heat, sweat rates, core temperatures, etc. I didn’t even realize how much a high core temperature can slow an athlete, not only on the run but on the bike as well. With more blood going to your skin for cooling, there’s less blood for your muscles--which means less oxygen and a slower pace. I also read everything I could find that Torbjorn Sinballe has written on the subject. I identified what my limiting factors would be for Kona 2010: high sweat rate, high core temperature and liquid absorption.

The athlete's stomach

I learned that an Ironman athlete’s stomach will only absorb about 45 oz. per hour—that’s 50 oz. less per hour than I sweat out. Experts disagree somewhat on this number but most are in that 40-50 oz. per hour range. I did figure out that my sweat rate on the bike is not as high as the run, so I planned to be able to come off the bike mostly hydrated--as long as I didn’t go too hard.

Since I would need so much liquid on the bike, I planned to consume all my calories as liquid. Drinking 200 oz. and eating solid food in a 5-hour period would have trashed my stomach. I kept track of everything I drank and ate on my key training sessions. I used this information to see a pattern develop for what worked the best.

Once the summer heat settled in, I was fine-tuning my nutrition plan. I experimented with increasing my calories and realized that 400 calories per hour on the bike was the maximum my stomach could handle at IM intensity. For my runs off the bike, I really had to practice getting in maximum liquids, even if I didn’t need it to get through a session. Even a short 20-to-30 minute run off the bike would include drinking 20+ oz. of race-day mixture. I even did some one-hour brick runs where I slammed 30 oz. in the first 20 minutes just to train my stomach. If I could do more in training than I needed in the race, then race day would be no problem. I even figured out which bottles would deliver the most liquid the easiest.

Core temperature

My core temperature was my other limiting factor. I had learned that being acclimated would be the one thing that would help me the most with the heat, so I arrived almost two weeks early.

Once in Kona, I experimented with some cooling clothing and didn’t notice any difference, so I went with the old-school skin suit I had been racing with. Practicing to stay cool was difficult. On some of my brick runs in the heat I would either carry a bottle of ice water to dump on my head or run a one-mile loop from my house, using my garden hose to douse myself on every loop. I did notice a big difference in how I felt. On actual race day, I took a minimum of one cup of ice at every aid station.

In my previous 15 Ironman races, I have never done anything to keep my core temperature down and stay cool. This time on the bike I opted for a vented helmet rather than aero and was fully doused at every aid station.

I entered T2 hydrated, relatively cool and ready to run. Keeping my effort easy to moderate was probably the most helpful. Even on sections of the run where I felt good, I kept my pace easy. I certainly could have run parts faster, but the risk would have been too high. As a result of sticking to my plan, I won my age group.

Kona 2010 was very rewarding not just for the win but for being able to focus on my limiting factors in regards to the heat and hydration, and then sticking with my race plan and seeing everything come together on race day. I have already identified additional weak areas to focus on for 2011.

When looking for improvement, we sometimes have to look at more than just our workouts and training schedules, and focus on what may be holding us back. 2011 will be another great adventure.

In 2010 Curt won his age group at IM World Championship in Hawaii and again five weeks later at 70.3 World Championships in Clearwater. Curt lives with his wife and daughter in Boulder, Colorado. He coaches for D3 Multisport with clients ranging from beginner to professional. He can be reached at [email protected]


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date: March 31, 2011

Curt Chesney